arrow

GH-37259: [Ruby] Add explicit csv gem dependency (#37506)

### Rationale for this change

The "csv" gem is a default gem for now but it will be a bundled gem in Ruby 3.4.
Bundled gem requires an explicit gem dependency.

This will cause failure when we do `require "csv"` in Ruby 3.4 (this means in master branch of Ruby = ruby 3.3.0dev for now). See examples in #37259.

### What changes are included in this PR?

Added `gem "csv"` in gemspec's runtime dependency of Red Arrow.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Users will use 'csv' gem from rubygems, not bundled, for Ruby < 3.4 .

* Closes: #37259

Authored-by: Hirokazu SUZUKI <heronshoes877@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>